chore(tmux-subagent): remove dead event-handler modules

Drop cleanup.ts, session-created-handler.ts, and session-deleted-handler.ts
which were never wired up; the lifecycle logic they contained lives inline
in TmuxSessionManager. Barrels trimmed to match.

src/features/tmux-subagent/cleanup.ts

@@ -1,42 +0,0 @@
-import type { TmuxConfig } from "../../config/schema"
-import { log } from "../../shared"
-import type { TrackedSession } from "./types"
-import { queryWindowState } from "./pane-state-querier"
-import { executeAction } from "./action-executor"
-
-export async function cleanupTmuxSessions(params: {
-  tmuxConfig: TmuxConfig
-  serverUrl: string
-  sourcePaneId: string | undefined
-  sessions: Map<string, TrackedSession>
-  stopPolling: () => void
-}): Promise<void> {
-  params.stopPolling()
-
-  if (params.sessions.size === 0) {
-    log("[tmux-session-manager] cleanup complete")
-    return
-  }
-
-  log("[tmux-session-manager] closing all panes", { count: params.sessions.size })
-  const state = params.sourcePaneId ? await queryWindowState(params.sourcePaneId) : null
-
-  if (state) {
-    const closePromises = Array.from(params.sessions.values()).map((tracked) =>
-      executeAction(
-        { type: "close", paneId: tracked.paneId, sessionId: tracked.sessionId },
-        { config: params.tmuxConfig, serverUrl: params.serverUrl, windowState: state },
-      ).catch((error) =>
-        log("[tmux-session-manager] cleanup error for pane", {
-          paneId: tracked.paneId,
-          error: String(error),
-        }),
-      ),
-    )
-
-    await Promise.all(closePromises)
-  }
-
-  params.sessions.clear()
-  log("[tmux-session-manager] cleanup complete")
-}